1. Field of the Invention
The present invention relates to a gearshift device for an automatic transmission installed on a vehicle.
2. Description of the Background Art
In recent years, as gearshift devices for automatic transmissions installed on vehicles, so-called shift-by-wire type gearshift devices have been proposed which are advantageous in reduction in operating force as well as size of the gearshift devices. The shift-by-wire type gearshift devices are such that a gear selection position where a gearshift lever is operated to be situated by the driver is detected by a sensor so that gear ranges of an automatic transmission (hereinafter, referred simply to AT) are changed over by an actuator based on a detection signal or such that the gear ranges of the AT are changed over through electric control (for example, refer to Japanese Patent Unexamined Publication No. JP-A-2001-341542).
Incidentally, in a gearshift device of JP-A-2001-341542, four sensors are arranged so as to match four gear selection positions, such as (N (neutral), R (reverse), D (drive),+(upshift),−(downshift)) of a gearshift lever, respectively. However, in the sensor arrangement like this, in the event that any of the sensors fails to thereby be unable to output a sensor signal, a gear range change in the AT corresponding to the gear selection position for which the failed sensor is arranged cannot be effected even when the gearshift lever is shifted into the relevant gear selection position.
To cope with this, there can be considered a configuration in which two or more sensors are arranged for each gear selection position in order to have redundancy, so that even though one of the sensors so arranged fails, the output of a sensor signal can be ensured. In this case, however, the number of sensors to be arranged increases at least twofold or more, and this increases the production costs.